Sometimes, planes get "stuck" to the ground (for lack of a better way to describe it). You can run them up to full throttle and they won't move. It also can happen to planes that can move if they come to a stop (once again, sometimes).
I have tried this as simple as possible and it seems repeatable. I have attached a simple mission on Stratis that has only vanilla assets in it. Jump in the closest russian plane and it should be stuck (I tried it twice now).